[PATCH v6 2/4] rust: generate a fatal error if BINDGEN_TARGET is undefined

[Nathan Chancellor]

On Tue, Dec 30, 2025 at 05:47:55PM +0100, Asuna Yang wrote:
> Generate a friendly fatal error if the target triplet is undefined for
> bindgen, rather than having the compiler generate obscure error messages
> during the build stage.
> 
> `BINDGEN_TARGET` is actually defined in `scripts/Makefile.rust`, but the
> file is included regardless of whether Rust is enabled, so perform this
> check in `rust/Makefile` to avoid breaking targets that do not yet
> support Rust builds.
> 
> This piece of code is copied from `scripts/Makefile.clang`.
> 
> Before this commit, error messages might look like:
> 
> error: unknown argument: '-mno-riscv-attribute'
> error: unsupported argument 'medany' to option '-mcmodel=' for target
> 'unknown'
> error: unsupported option '-march=' for target ''
> error: unsupported option '-mno-save-restore' for target ''
> error: unknown target triple 'unknown'
> panicked at bindgen/ir/context.rs:562:15:
> libclang error; possible causes include:
> - Invalid flag syntax
> - Unrecognized flags
> - Invalid flag arguments
> - File I/O errors
> - Host vs. target architecture mismatch
> 
> Acked-by: Miguel Ojeda <ojeda at kernel.org>
> Signed-off-by: Asuna Yang <xinrui.riscv at isrc.iscas.ac.cn>
> ---
>  rust/Makefile | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/rust/Makefile b/rust/Makefile
> index 2603b34f9833..37b4205afb70 100644
> --- a/rust/Makefile
> +++ b/rust/Makefile
> @@ -385,6 +385,12 @@ bindgen_skip_c_flags := -mno-fp-ret-in-387 -mpreferred-stack-boundary=% \
>  	-fzero-init-padding-bits=% -mno-fdpic \
>  	--param=% --param asan-% -fno-isolate-erroneous-paths-dereference
>  
> +# Because scripts/Makefile.rust is included regardless of whether Rust is enabled,
> +# we perform this check here to avoid breaking targets that do not yet support Rust builds.

This might read a little better if it were

  scripts/Makefile.rust is included ..., so we perform ...

instead of

  Because ..., we perform ...

or at the very least reversing the phrases

  We perform ... because ...

But that could just be personal preference.

> +ifeq ($(BINDGEN_TARGET),)
> +$(error add '--target=' option to scripts/Makefile.rust)
> +endif
> +
>  # All warnings are inhibited since GCC builds are very experimental,
>  # many GCC warnings are not supported by Clang, they may only appear in
>  # some configurations, with new GCC versions, etc.
> 
> -- 
> 2.51.1
>